A.u. of Action (a.u.) is a unit in the category of Angular momentum, Action. It is also known as atomic units, u.a., au, ua. This unit is commonly used in the a.u. unit system. A.u. of Action (a.u.) has a dimension of ML2T-1 where M is mass, L is length, and T is time. It can be converted to the corresponding standard SI unit J-s by multiplying its value by a factor of 1.05457266E-034.